There are definitely good and bad ways to handle this.

Bad: SEA-FAI a couple years ago. The dreaded day-of downgrade from a 739 to 738. App auto populated from First to a middle seat in an almost toilet row. No page from the desk, nothing. Went to go ask about it and was told in so many words to deal with it. Bad.

Good: PDX-ANC-FAI with confirmed upgrades on both segments. PDX-ANC delayed, and would have caused a misconnect in ANC. Gate agent proactively tracked me down and waived the MCT time in SEA to get me to FAI at pretty much the same time, albeit in coach. Had a 30 minute connect in SEA, they knew I was coming, and shut the door after me. Good.